Manufacture of piston rings



March 3, 1936. M. B. COVERT I 2,033,093

MANUFACTURE of PISTON RINGS Filed June 8, 1933 Patented Mar. 3, 1936UNl'lED STATES PATENT HQE MANUFACTURE or PISTON mes Martin B. Covert,Holland, Mich., assignor to Renu Parts Corporation, Holland, Mich., acorporation of Michigan Application June 8, 1933, Serial No. 674,928

3 Claims.

the same diameter and cross section as required for the piston ringcasting. To provide for outward pressure of the piston ring when it isinstalled on a piston reciprocal in a cylinder the pattern is split andthe ends expanded and then an insert or slug is positioned between theends thereby throwing the pattern, and then, consequently, a castingmade in a mold formed by the pattern, out of round. In the finishing ofa ring so cast the insert or slug is cut away and then when the ring isinstalled on a piston it is compressed to substantially circular formbut the innate forces therein tend to restore it to its cast shape andtherefore the ring forcibly bears against the cylinder wall. However,the pressure exerted on the cylinder wall by a ring made in this manneris not uniform for the pressure is relatively high adjacent the splitbut is quite low adjacent the part of the ring diametrically oppositethe split. If a ring is cast in truly circular form and thensubsequently split and expanded it exerts substantially uniform pressureon a cylinder wall when in operating position. One of the objects of myinvention is to expedite the manufacture of piston rings which exertsubstantially uniform pressure on a cylinder wall.

It is difficult to cast a piston ring of small crosssectional areabecause the heavy molten metal often will not uniformly flow through asmall mold cavity. However, the molten metal will flow satisfactorilythrough a narrow but elongated cavity, that is to say, it is notdifficult to cast a sleeve having a thin wall in contradistinction tocasting a ring of small cross-sectional area. In casting an elongatedsleeve, in an ordinary mold, the impurities in the iron rise to the topof the mold cavity and often the upper end of the sleeve is of a poorgrade of metal because of this. Furthermore, when sleeves are cast insand molds, hard spots are found to be prevalent due to moisture in thesand which chills the hot metal. Such castings are also found to besubject to foundry strains as well as the hard spots and otherobjectionable characteristics. However, in the manufacture of pistonrings, sleeves having a thin wall have been cast and piston ring blankshave been cut therefrom. Such blanks have not been iuiiform because ofthe above set forth diflicultie's encountered in casting a sleeve. It isthereforeanother object of my invention to so sired thickness.

cast a sleeve that substantially uniform piston ring blanks can besubsequently cut therefrom.

A further object is to heat treat the sleeve prior to the time it isdivided into ring blanks so as to free the sleeve of foundry strains,hard spots and the like to thereby insure that the rings into which thesleeve is divided will have uniform metallurgical characteristics.

A still further object is to split and expand the sleeve prior todividing it into rings and to impart a permanent set to the sleeve sothat rings cut therefrom will exert uniform pressure on the cylinderwall when installed on a piston in a cylinder.

In the following description reference is made to the accompanyingdrawing wherein Fig. 1. is a perspective view illustrating a cast sleevedivisible into piston ring blanks;

Fig. 2 is a perspective view showing the sleeve inan intermediate stepin the manufacture of the rings; and r Fig. 3 is a perspective view of asleeve ready to be divided into ring blanks and illustrating the mannerin which the sleeve is so divided.

The preferred embodiment of my invention resides in first providing apermanent mold either of metal or refractory material and having a moldcavity of an outside diameter substantially equal to the desired outsidediameter of the ring blank, and wherein the cavity is of such a lengththat a sleeve cast therein may be divided evenly into a predeterminednumber. of ring blanks of a de- The width of the cavity is substantiallyequal to the desired width of the ring blanks into which the sleeve isto be divided. Each of the dimensions may be slightly greater thandesired in the finished rings so that there will be sufficient metal topermit the finishing operations on the ring blanks.

The sleeves are preferably cast. in the molds under a centrifugal actionso that the metal will be uniformly distributed throughout the moldcavities which therefore prevents the collection of impurities in themetal in any one part of the cavities and because of this the castsleeves are substantially uniform throughout. A sleeve so cast isindicated by d in the accompanying drawing.

The next step in is to slit to then expand the same. The slit is spreadand spacing bar 6 is inserted in the slit to retain the the manufactureof the rings the sleeve axially, as indicated at 5, and

expanded sleeve out of round, that is to say, to

retain the sleeve in an eccentric shape.

After the sleeve has been expanded out of round it is heated to atemperature above that to which the rings will be subjected in use toimpart a permanent set to the sleeve in the out of round shape, that isto say, to set the tension of the metal. This heat treatment alsoremoves foundry strains, hard spots and the like, if any are present,and produces uniform hardness throughout the sleeve.

After the sleeve has been heated for a sufficient length of time toimpart the permanent set, it is permitted to cool and the spacing bar 6is then removed. The sleeve will then appear as illustrated in-Fig. 3,that is to say, the ends thereof adjacent the slit will be spaced apartafter removal of the spacing bar and the sleeve will be slightly out ofround. The sleeve is then clamped in a suitable machine tool, such as alathe, and individual ring blanks are cut therefrom at spaced intervalssuch as, for example, those indicated by the broken lines I in Fig. 3.Preferably the sleeve is of such a length that it may be divided into anumber of ring blanks of uniform thickness;

After the ring blanks have been cut from the sleeve the finishingoperations are performed, such as machining or grinding to size,slotting to provide oil grooves, filing to remove burrs, or any otherdesired operation.

My novel method for manufacturing piston rings may be summarized asconsisting in casting a sleeve having substantially uniformmetallurgical characteristics throughout; axially slitting the sleeve;expanding the sleeve to an eccentric shape and holding it in thiseccentric shape; subjecting it to a temperature above that to which therings will be subjected in use for a sufficient period of time to imparta permanent set to the sleeve when cooled; permitting the sleeve tocool; and then dividing the sleeve into ring blanks and subsequentlyperforming the. de sired finishing operations thereon.

Since the sleeve is cast under a centrifugal action the impurities areprevented from collecting in any one part of the sleeve, and since thesleeve is subjected to such a heat treatment that undesirablemetallurgical characteristics such as foundry strains and hard spots areremoved, it is manifest that the sleeve may be divided into a number ofring blanks having substantially uniform metallurgical characteristics.Furthermore, since the sleeve is cast round and subsequently expandedout of round and then given a permanent set in the out of round oreccentric shape, the

rings made from blanks cut from this sleeve will exert substantiallyuniform pressure against the cylinder wall when. arranged in operatingposition on a piston in a cylinder.

I have illustrated and described the preferred manner of practice for mynovel method for the manufacture of piston rings but it is to beunderstood that this is capable of variation and modification and Itherefore do not wish to be limited to the precise details set forth butdesire to avail myself of such changes and alterations as fall withinthe purview of the following claims.

I claim:

1. The method of manufacturing uniform piston rings of thin crosssection which consists in casting a sleeve of a thickness substantiallyequal to one cross sectional dimension of the piston rings, axiallyslitting the sleeve, installing a spacing bar in the sleeve to expandthe sleeve to an eccentric shape, heating the expanded sleeve to atemperature above that to which the rings will be subjected in use toremove foundry strains, hard spots and the like from the sleeve and toimpart a permanent set to the sleeve, and then dividing the sleeve atspaced intervals substantially equal to the other cross sectionaldimension of the rings to provide uniform ring blanks on which finishingoperations may be subsequently performed.

2. The method of manufacturing uniform piston rings or the like whichincludes axially slitting a metallic sleeve, installing a spacing bar inthe slit to expand the sleeve to an eccentric shape, heating theexpanded sleeve to a temperature above that to which the rings will besubjected in use to remove strains, hard spots and the like from thesleeve and to impart a permanent set to the sleeve, and then dividingthe sleeve into ring blanks on which finishing operations may besubsequently performed.

3. The method of manufacturing a metallic sleeve which may be dividedinto uniform ring blanks or the like which consists in forming a sleeve,subsequently axially slitting the metallic sleeveand expanding the slitsleeve to an eccentric shape, and heating the expanded sleeve to atemperature above that to which the ring blanks or the like willbe'subjected in use to re-,

move strains, hard spots and the like from the sleeve andto impart apermanent set to the sleeve.

MARTIN B. COVERT.

